pr/plugin config filename in AbstractPlugin

Quote from i-MSCP Github (1.5.3)

Code

1. pr/plugin config filename in AbstractPlugin
3. - Change to use the file "config.php" as the name of the per
4. plugin configuration file. Introduced in a28626c

Source: https://github.com/i-MSCP/imsc…5f23e4ec951a0002df81fe6bc